The present invention relates to a method for the preparation of a bonding tool to be employed for preparing semiconductor devices or their parts.
More particularly, the present invention relates to a method for the preparation of a bonding tool which can be employed for bonding lead wires to workpieces for semiconductor devices, including an integrated circuit (IC) and the like, by the use of tape automated bonding (TAB), the bonding tool comprizing a body of a super hard material as a tool-head which is to be in contact with a workpiece under machining by using the bonding tool and a shank to which the tool-head made of the super hard material is bonded by brazing with a specified brazing composition, the bonding tool having advantageous characters; i.e., those including that a brazing strain is so small that the tool-head made of the super hard material rarely cracks, and that the bond strength between the shank and the tool-head made of the super hard material is extremely high.
Bonding tools for tapeautomated bonding (TAB) are tools to be employed for bonding, at a time by thermocompression, an array of lead wires integrated onto a tape carrier to a workpiece for a semiconductor part, such as IC, etc.. The bondings of the workpiece by the use of a bonding tool are usually conducted under severe conditions; i.e., at such high temperatures as those of 500.degree. C. to 600.degree. C. and under repeating high loading conditions, the workpiece being in contact with the tool-head of the bonding tool. Therefore, a material having a high heat resistance, a high abrasion resistance, a high heat conductivity, and an adhesion-resisting property against a brazing material, especially a single crystal of diamond, has preferably been used as a material for a tool-head of a bonding tool.
Several attempts and proposals have been made to prepare a bonding tool for TAB by using a single crystal of daimond as a material for the tool-head of the bonding tool. These known methods include:
(A) a method for preparing a bonding tool whose typical structure is schematically illustrated in FIG. 2, comprizing the step of mounting a single crystal of diamond to be used as a tool-head 1 to a shank 6 through a sintered body of metal powder 5 wherein the tool-head 1 is supported, usually only mechanically by the shrinkage forces of the sintered body of metal powder 5, in the hole of the sintered body of metal powder 5; and
(B) a method for preparing a bonding tool whose typical structure is schematically illustrated in FIG. 3, comprizing the step of bonding by brazing a single crystal of diamond to be used as a tool-head 1 to a shank 4 made of tungsten or molybdenum having a low thermal expansion coefficient with a conventional brazing material 2, such as a titanium-containing silver solder, a tantalum-containing gold solder, etc.
In the place of the single crystal of diamond, other kinds of super hard materials, including diamond compacts, CBN compacts, cemented carbides, molybdenum, and the like, have also been used as a material for the tool-head of a bonding tool in the prior art methods.
However, those known for the preparation of a bonding tool for TAB have a variety of disadvantages and are not always satisfactory.
For example, one of the serious disadvantages of the method (A) wherein the tool-head 1 made of a single crystal of diamond is only mechanically supported is that this method requires a larger diamond grit compared to other methods in the preparation of a bonding tool and another serious disadvantage of this method is that the bonding tools prepared thereby have serious problems; i.e., those including that the tool-head 1 made of a single crystal of diamond sometimes slips or shakes in the hole of the sintered body of metal powder 5 and tends to come off therefrom under machining in the use of the thus prepared bonding tools. It is possible to support strongly the tool-head 1 made of a single crystal of diamond with the sintered body of metal powder 5 by reacting them with each other at their interface at high temperatures even when the method (A) is employed; however, in this case, there will be other serious problems, such that the occurrence on a crack in the single crystal of diamond cannot be avoided and so on.
On the other hand, the method (B) in which a single crystal of diamond is bonded by brazing in vacuum to a shank made of tungsten or molybdenum having a low thermal expansion coefficient by the use of a conventional titanium-containing silver solder as a brazing material, has such a disadvantage in that a large distortion or cracking of the tool-head made of a single crystal of diamond is caused by the combination of shrinkage stress induced by solidification of the brazing material used and stress based on the thermal expansion or shrinkage of the shank in the thus prepared bonding tools, although the brazing strengh may be improved by the action of the titanium which is added.
If a conventional tantalum-containing gold solder is used in the place of the titanium-containing silver solder in the method described above, the distortion of the tool-head made of a single crystal of diamond may be small and the occurrence of a crack in the single crystal of diamond may be suppressed; however, this method also has problems, including that the tool-head made of a single crystal of diamond tends to come off from the shank because the brazing strength of a tantalum-containing gold-solder is much lower than that of a titanium-containing silver solder and is not high enough for practical use.